Vehicles such as automobiles are generally provided with a seat belt apparatus that restrains an occupant in a seat including a seat portion in which the occupant is seated and a backrest portion located behind the occupant. Such a seat belt apparatus includes a webbing that restrains an occupant, a seat belt retractor that retracts the webbing, a guide anchor that is provided on the vehicle body side and that guides the webbing, a belt anchor that fixes the webbing to the vehicle body, a buckle disposed on the side of the seat, and a tongue disposed on the webbing, and restrains the occupant in the seat with the webbing by fitting the tongue into the buckle. In such a seat belt apparatus, one end of the webbing is fixed to the belt anchor, and the other end of the webbing is passed through the guide anchor and is connected to the seat belt retractor.
It is becoming common that such a seat belt retractor includes a locking mechanism that stops the withdrawal of the webbing when the vehicle is inclined or rapidly decreased in speeds in a vehicle collision or the like, and a pretensioner that takes up the slack in the webbing in a vehicle collision or the like (see, for example, Patent Literature 1 and Patent Literature 2).
In the seat belt retractor described in Patent Literature 1, a locking mechanism (4, 5) is disposed on one outer side (1A) of a base frame (1), a pretensioner (10) including driving means (11, 12, 15) and the like is disposed on the other outer side (1B) of the base frame (1), and a spring unit (8) is disposed on the outer side thereof. A pretensioner plate (31) for rotatably supporting a spool is disposed between the base frame and the pretensioner.
In the seat belt retractor described in Patent Literature 2, a spring unit is disposed on one outer side of a base frame (8), a pretensioner including a drive unit (7) is disposed on the other outer side of the base frame (8), and a locking mechanism including a pawl (4) and a control unit (10) is disposed on the outer side thereof. A bearing ring (13) for rotatably supporting a spool is disposed between the base frame and the pretensioner.